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//---------------------------------------------------------------------------------------------------- Impl
impl<T: AsRef<str>> HeadTail for T {}

//---------------------------------------------------------------------------------------------------- Head
/// Head/Tail characters of a [`str`]
///
/// This trait provides some functionality for
/// cutting off a string either by the head, tail,
/// or both, with optional `...` after/before/in-between.
///
/// Anything that implements `AsRef<str>` can use this trait.
pub trait HeadTail: AsRef<str> {
	/// Return the first `len` bytes of this [`str`].
	///
	/// This will return the full [`str`] if the `len` is
	/// longer than the actual inner [`str`].
	///
	/// ## Note
	/// Input is split by [`char`]'s, not bytes.
	fn head(&self, len: usize) -> &str {
		let s = self.as_ref();

		if let Some((index, _)) = s.char_indices().nth(len) {
			&s[..index]
		} else {
			s
		}
	}

	/// Same as [`head()`] but the [`String`] ends with `...`
	///
	/// This will return the full string without `...` if
	/// the `len` is longer than the actual inner [`str`].
	///
	/// ## Note
	/// Input is split by [`char`]'s, not bytes.
	fn head_dot(&self, len: usize) -> String {
		let s = self.as_ref();

		if let Some((index, _)) = s.char_indices().nth(len) {
			format!("{}...", &s[..index])
		} else {
			String::from(s)
		}
	}

	/// Return the last `len` bytes of this [`str`].
	///
	/// This will return the full [`str`] if the `len` is
	/// longer than the actual inner [`str`].
	///
	/// ## Note
	/// Input is split by [`char`]'s, not bytes.
	fn tail(&self, len: usize) -> &str {
		let s = self.as_ref();

		let end = s.chars().count();

		if len >= end {
			return s;
		}

		if let Some((index, _)) = s.char_indices().nth(end - len) {
			return &s[index..];
		}

		s
	}

	/// Same as [`tail()`] but returns a [`String`] starting with `...`
	///
	/// This will return the full string without `...` if
	/// the `len` is longer than the actual inner [`str`].
	///
	/// ## Note
	/// Input is split by [`char`]'s, not bytes.
	fn tail_dot(&self, len: usize) -> String {
		let s = self.as_ref();

		let end = s.chars().count();

		if len >= end {
			format!("...{s}");
		}

		if let Some((index, _)) = s.char_indices().nth(end - len) {
			return format!("...{}", &s[index..]);
		}

		format!("...{s}")
	}

	/// Return the first `head` bytes and last `tail`
	/// bytes of this string separated with `...`.
	///
	/// ## Note
	/// Input is split by [`char`]'s, not bytes.
	fn head_tail(&self, head: usize, tail: usize) -> String {
		let s = self.as_ref();

		let end = s.chars().count();

		if head >= end || tail >= end || head + tail >= end {
			return String::from(s);
		}

		// Iterator is consumed, must create twice.
		let head = s.char_indices().nth(head);
		let tail = s.char_indices().nth(end - tail);

		if let (Some((head, _)), Some((tail, _))) = (head, tail) {
			return format!("{}...{}", &s[..head], &s[tail..]);
		}

		String::from(s)
	}
}

//---------------------------------------------------------------------------------------------------- TESTS
#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn _head() {
		let four_bytes = "desu";
		let six_bytes  = "です";

		assert!(four_bytes.len() == 4);
		assert!(six_bytes.len()  == 6);

		assert!(four_bytes.head(2) == "de");
		assert!(six_bytes.head(1) == "で");
	}

	#[test]
	fn _head_dot() {
		let four_bytes = "desu";
		let six_bytes  = "です";

		assert!(four_bytes.len() == 4);
		assert!(six_bytes.len()  == 6);

		assert!(four_bytes.head_dot(2) == "de...");
		assert!(six_bytes.head_dot(1) == "で...");
	}

	#[test]
	fn _tail() {
		let four_bytes = "desu";
		let six_bytes  = "です";

		assert!(four_bytes.len() == 4);
		assert!(six_bytes.len()  == 6);

		assert!(four_bytes.tail(2) == "su");
		assert!(six_bytes.tail(1) == "す");
	}

	#[test]
	fn _tail_dot() {
		let four_bytes = "desu";
		let six_bytes  = "です";

		assert!(four_bytes.len() == 4);
		assert!(six_bytes.len()  == 6);

		assert!(four_bytes.tail_dot(2) == "...su");
		assert!(six_bytes.tail_dot(1) == "...す");
	}

	#[test]
	fn _head_tail() {
		let eight_bytes = "desukedo";
		let twelve_bytes  = "ですけど";

		assert!(eight_bytes.len() == 8);
		assert!(twelve_bytes.len()  == 12);

		assert!(eight_bytes.head_tail(2, 2) == "de...do");
		assert!(twelve_bytes.head_tail(1, 1) == "で...ど");

		assert!(eight_bytes.head_tail(4, 4) == "desukedo");
		assert!(twelve_bytes.head_tail(2, 2) == "ですけど");
	}
}